Method and apparatus for providing input emi filtering in power supplies

ABSTRACT

A power supply electromagnetic interference (EMI) filter circuit and technique. In one embodiment, a method of filtering EMI in a power supply includes rectifying an AC signal from an AC source, smoothing the rectified AC signal with a bulk storage capacitor to provide a DC output as an input to a power conversion circuit and filtering the EMI generated by the power conversion circuit from reaching the AC source by using the bulk capacitor and one or more inductors in combination with the AC source capacitance as an EMI filter. In one embodiment the method also includes the use of one or more of the inductors as a fusing element.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to power supplies and,more specifically, the present invention relates to a switched modepower supply with an input electromagnetic interference (EMI) filtercircuit.

[0003] 2. Background Information

[0004] Electronic devices use power to operate. Switched mode powersupplies or adapters are widely used to power electronic products aswell as charge batteries used to power mobile products such as forexample wireless phones, palm top computers, toys, etc. Switched modepower supplies generate EMI, which must be filtered to allow the powersupply to meet national and international standards stipulatingacceptable levels of EMI. This requires that the switched mode powersupply include components at the input of the power supply that filterEMI in order to meet these standards. Furthermore, an input fuse isrequired to meet national and international safety standards.

[0005] Known power supply techniques employ input EMI filter circuits ofvarying complexity. The simplest form of input EMI filter is known as api filter and is used in low-power power supplies to reduce power supplycost. The fuse is a separate component, which is typically eitherdesigned solely for use as a fuse or as a resistor specifically designedto meet national and international safety standards as a fusiblecomponent.

SUMMARY OF THE INVENTION

[0006] A power supply input EMI filter circuit is disclosed. In oneembodiment, a method of filtering EMI in a power supply includesrectifying an AC signal with a rectifier, smoothing the rectified signalwith a bulk storage capacitor to provide a DC output as an input to apower conversion circuit and filtering the EMI generated by the powerconversion circuit from reaching the AC source by using the bulkcapacitor and one or more inductors in combination with the AC sourcecapacitance as an EMI filter. In one embodiment the method also includesthe use of one or more of the inductors as a fusing element to meetsafety requirements. Additional features and benefits of the presentinvention will become apparent from the detailed description and figuresset forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The present invention detailed illustrated by way of example andnot limitation in the accompanying figures.

[0008]FIG. 1 is a schematic illustrating a power supply input circuitincluding a fuse and input EMI filter circuit.

[0009]FIG. 2 is a schematic illustrating one embodiment of a powersupply with a simplified input EMI filter circuit and fuse in accordancewith the teachings of the present invention.

[0010]FIG. 3 is a schematic illustrating another embodiment of a powersupply with a simplified input EMI filter and fuse circuit in accordancewith the teachings of the present invention.

[0011]FIG. 4A provides an illustration of one embodiment of a full waverectifier utilizing a diode bridge in accordance with the teachings ofthe present invention.

[0012]FIG. 4B provides an illustration of one embodiment of a half waverectifier utilizing a single diode on one of the rails in accordancewith the teachings of the present invention.

[0013]FIG. 4C provides an illustration of one embodiment of a half waverectifier utilizing a single diode on each of the rails in accordancewith the teachings of the present invention.

[0014]FIG. 4D provides an illustration of one embodiment of a half waverectifier utilizing a plurality of diodes on at least one of the railsin accordance with the teachings of the present invention.

[0015]FIG. 5 is a schematic illustrating yet another embodiment of apower supply with a simplified input EMI filter and fuse circuit inaccordance with the teachings of the present invention.

[0016]FIG. 6 is a schematic illustrating still another embodiment of apower supply with a simplified input EMI filter and fuse circuit inaccordance with the teachings of the present invention.

DETAILED DESCRIPTION

[0017] A novel technique to reduce the cost of input EMI filtercircuitry in switched mode power supplies is disclosed. In the followingdescription, numerous specific details are set forth in order to providea thorough understanding of the present invention. It will be apparent,however, to one having ordinary skill in the art that the specificdetail need not be employed to practice the present invention. In otherinstances, well-known materials or methods have not been described indetail in order to avoid obscuring the present invention.

[0018] In one embodiment, the present invention provides a simplifiedinput EMI circuit, which therefore reduces the cost and complexity ofinput EMI filter circuitry and the fuse function.

[0019] To illustrate, FIG. 1 shows a schematic of a power supply inputstage including a fuse 101, a rectifier circuit 100 and EMI filtercircuitry including capacitors 103 and 104 and an inductor 105. Theinput EMI filter circuitry is coupled in a configuration that is knownas a pi filter, which can be appreciated to one skilled in the art. Ascan be appreciated by one skilled in the art, the rectifier circuit 100can be either a well-known full or half wave rectifier circuit. If afull wave rectifier circuit is used, the rectification bridge ofrectifier circuit 100 can be constructed using either discrete diodes ora single component bridge rectifier. If a half wave rectifier circuit isused, the rectifier circuit 100 can be constructed using a single diodeor multiple diodes coupled in series. The latter construction is used incertain embodiments to reduce EMI and or to increase the amount of inputvoltage surges that rectifier circuit 100 can withstand, as will beappreciated to one skilled in the art.

[0020] The circuitry shown in FIG. 1 has an AC source 102 at the inputand provides a rectified and smoothed or filtered DC output voltage atDC output 106. Such a configuration is typical of low power AC to DCpower supply circuits such as those employed in low power (<10 Wattsoutput) adapters and chargers for consumer electronics items and thelike. As well as forming part of the pi filter, capacitors 103 and 104also provide bulk storage of charge derived from the AC source 102 whenthe voltage across the AC source 102 is greater than the DC voltageacross capacitors 103 and 104. When this condition is met, current flowsfrom the AC source 102 through capacitors 103 and 104. The charge thusstored on capacitors 103 and 104 provides a relatively stable DC outputvoltage at DC output 106 as required for efficient operation of a powerconversion circuit that is to be coupled to receive the DC outputvoltage at DC output 106.

[0021] The fuse 101 shown in FIG. 1, which is coupled between AC source102 and rectifier circuit 100 is a fusible resistor. In order for aresistor to fulfill the international standards required of a fusecomponent, the resistor is normally of a wore wound construction andcovered in a flame retardant or heatshrink material that prevents piecesof the resistor being scattered when the fuse 101 is blown during afault condition. The position of the fuse 101 is also important toensure compliance of the power supply with international safetystandards.

[0022] To comply with international safety standards, the fuse 101 mustbe positioned such that it becomes an open circuit in the event of anabnormally high current being drawn from AC source 102 due to a fault onany component in the rectifier circuit 100, EMI filter consisting ofcomponents 103, 104 and 105 or any component in the power supply circuitcoupled to DC output 106. FIG. 1 therefore shows the most obviousposition for fuse 101 to ensure that it limits an abnormal current inthe case of a fault in any component coming after fuse 101.

[0023]FIG. 2 shows a schematic illustrating one embodiment of a powersupply input stage utilized in a power supply in accordance with theteachings of the present invention. In the illustrated embodiment, an ACsignal from an AC source 102 is rectified by rectifier circuit 200 andis then smoothed at DC output 106 by capacitor 203. The circuit shown isa simplification of that shown in FIG. 1 through the elimination of thefuse 101 and also one of the bulk storage capacitors 103 and 104. In thecircuit embodiment of FIG. 2, the input fuse function is provided byinductor 202, which also forms part of an EMI filter as described later.As can be appreciated to one skilled in the art, typical input inductorcomponents used in power supplies, such as for example below 10 Wattsoutput, are typically constructed of a fine wire wound on a ferritecore. As such the construction is similar to the fusible resistor 101described above. As such, by the correct choice of wire gauge(diameter), inductor 202 can be designed to become an open circuit underspecific conditions of abnormal current flow such as those due to afault in one of the power supply components. In one embodiment, theposition of inductor 202, in common with the fuse 101 in FIG. 1, is onthe AC source 102 side of the rectifier circuit 200 to ensure circuitprotection under any of the abnormal current conditions as describedearlier.

[0024] The EMI filter configuration of the circuit in FIG. 2 forms a pifilter with the single bulk storage capacitor 203, inductor 202 and ACsource capacitance 201 of AC source 102. It is appreciated that ACsource capacitance 201 is a distributed source capacitance of AC source102, rather than a specific component. This AC source capacitance 201 ispresent in every AC source 102 and is represented by an equivalentcapacitance in the equipment used to make EMI measurements. Thisequipment is called a Line Impedance Stabilization Network (LISN), aswill be familiar to one skilled in the art. The AC source or LISNcapacitance can therefore be specifically used to form a pi filter withthe simplified input circuitry of FIG. 2 in accordance with theteachings of the present invention. Since EMI measurements are madeunder standardized conditions of input cable length and LISN circuitry,the AC source capacitance 201 is deterministic and provides repeatablemeasurements to ensure consistent EMI filter performance.

[0025] As shown in the depicted embodiment, rectifier circuit 200 iscoupled between inductor 202 and capacitor 203. In one embodiment, thecapacitance value of capacitor 203 is not necessarily equal to the valueof capacitance 104 of FIG. 1. In the depicted embodiment, capacitor 203is a single capacitor and is adapted to provide the bulk storagefunction and is therefore usually a larger value of capacitance valuethan that of capacitor 104 to achieve the same average DC output voltageat DC output 106. However, despite typically being a larger capacitor,the elimination of one bulk storage capacitor typically provides asignificant cost saving over the configuration in FIG. 1 since the costof each capacitor component is strongly influenced by the packagingitself, which is reduced using a single component. Furthermore, theelimination of one bulk storage capacitor reduces the cost of circuitassembly in production by reducing component count. In one embodiment,inductor 202 also does not necessarily the same inductance value asinductor 105 and is chosen in each case to optimize the pi filterperformance with the AC source capacitance 201 and bulk storagecapacitor 203. In operation, the rectified and smoothed or filtered DCvoltage at DC output 106 is received by power conversion circuit 208,which generates an output voltage at power conversion circuit output210. In one embodiment, power conversion circuit 208 is a switched modepower converter and the EMI filter circuit of FIG. 2 is employed tofilter the EMI in accordance with the teaching of the present invention.

[0026]FIG. 3 shows a schematic illustrating another embodiment of apower supply input stage employed in a power supply in accordance withthe teachings of the present invention. The circuit shown is again asimplification of that shown in FIG. 1 through the elimination of thefuse 101 and also one of the bulk storage capacitors 103 and 104. In thecircuit of FIG. 3, the input fuse function is provided by inductor 302,which also forms part of the EMI filter.

[0027] In this configuration however, the inductor 302 is placed on theoutput side of the rectifier circuit 300. That is, rectifier circuit 300is between AC source 102 and inductor 302. In one embodiment, thisplaces a limitation on the type of input rectifier circuit 300 that canbe used if the inductor is also required to perform the fuse function.This limitation arises since connection of inductor 302 can only providea fuse function in compliance with international safety standardsdescribed earlier if the input rectifier circuit 300 is a half waverectifier circuit. As can be appreciated by one skilled in the art, ifinput rectifier circuit 300 is a full wave bridge rectifier circuit, theshort circuit failure of any one of the diodes in the rectificationbridge will cause abnormally high current to be drawn from AC source 102without this current flowing through inductor 302. In one embodiment,the circuit shown in FIG. 3 is therefore limited to use when inputrectifier circuit 300 is a half wave rectifier circuit if the inductoris also required to function as a fuse.

[0028] To illustrate, FIGS. 4A, 4B, 4C and 4D provide various exampleschematics of various embodiments of rectifiers that may be utilized inaccordance with the teachings of the present invention. In particular,FIG. 4A provides an illustration of one embodiment of a full waverectifier utilizing a diode bridge. FIG. 4B provides an illustration ofone embodiment of a half wave rectifier utilizing a single diode on oneof the rails. FIG. 4C provides an illustration of one embodiment of ahalf wave rectifier utilizing a single diode on each of the rails. FIG.4D provides an illustration of one embodiment of a half wave rectifierutilizing a plurality of diodes on at least one of the rails. It isappreciated that other suitable variations of the schematics illustratedin FIGS. 4A, 4B, 4C and 4D may be utilized in accordance with theteachings of the present invention. Any one of the rectifier circuitsshown could be used in the circuits of FIG. 2, 3 or the circuitsdescribed below though their application is not limited to only thoseconfigurations shown in FIGS. 4A, 4B, 4C and 4D.

[0029] As illustrated in FIGS. 4B, 4C and 4D, embodiments of the halfwave rectifier circuit can be constructed using a single diode ormultiple diodes coupled in series. When using multiple diodes, one ormore diodes can be connected on either or both AC input rails. Using oneor more diodes on both rails of the AC input reduces EMI by blocking theEMI generated by the power conversion circuit from being coupled to theAC source on both rails during times when the diodes are not conducting.

[0030] As will be appreciated by one skilled in the art, in oneembodiment, the configuration of FIG. 3 can be used with rectifiercircuit 300 as a full wave rectifier circuit, such as for example therectifier illustrated in FIG. 4A, if a separate fuse component is usedcoupled in series with the AC source 102 on the input side of rectifiercircuit 300. In this embodiment, inductor 302 no longer provides thefuse function and the circuit complies with international safetystandards.

[0031] Referring back to the embodiment of FIG. 3, an AC signal isprovided by AC source 102 and is rectified by rectifier circuit 300 andsmoothed by capacitor 303 such that a rectified and smoothed or filteredDC signal is generated at DC output 106. The rectified and smoothed DCsignal at DC output 106 is coupled to be received by power conversioncircuit 208 such that an output is generated at power conversion output210. In one embodiment, power conversion circuit 208 is a switched modepower converter.

[0032] The EMI filter function in the embodiment of FIG. 3 is made up ofinductor 302, bulk storage capacitor 303 and AC source capacitance 201of AC source 102. In common with the embodiment of FIG. 2, the AC sourceor LISN capacitance is used to form a pi filter with the simplifiedinput circuitry of FIG. 3. Other benefits of the simplified inputcircuitry of FIG. 3 are common with those of the circuit illustrated inFIG. 2 as described previously.

[0033]FIG. 5 shows a schematic illustrating yet another embodiment of apower supply input stage of a power supply in accordance with theteachings of the present invention. In the embodiment depicted in FIG.5, the general configuration and functionality share similarities withthe embodiment shown and described with respect to FIG. 2. An AC signalis output by AC source 102 and it is rectified by rectifier 500 andsmoothed or filtered by capacitor 503 to provide a DC signal at DCoutput 106 at capacitor 503. Power conversion circuit 208 receives therectified and smoothed DC signal at DC output 106 such that an output isprovided at power conversion circuit output 210.

[0034] Two inductors 502 and 504, however, have replaced the inputinductor 202 of the embodiment of FIG. 2. In the illustrated embodiment,inductors 502 and 504 are coupled between AC source 102 and rectifiercircuit 500. In one embodiment, the total inductance of inductors 502and 504 is not necessarily equal to the inductance of inductor 202. Forinstance, in one embodiment, one of the inductors 502 and 504 could bedesigned specifically to have different impedance versus frequencycharacteristics than the other in order to filter specific EMIfrequencies more efficiently. In this embodiment either one or both ofinductors 502 and 504 can act as a fuse. Typically the lowest costsolution is to design only one of the inductors 502 and 504 to act as afuse in order that only one has the flame retardant or heatshrinkcovering to comply with international safety standards as a fusecomponent. This can be accomplished, for example, by using a thinnerwire on the inductor that is to function as fuse than the wire used onthe other inductor.

[0035]FIG. 6 shows a schematic illustrating still another embodiment ofa power supply input stage used in a power supply in accordance with theteachings of the present invention. In FIG. 6, the general configurationand functionality share similarities with the circuit shown in FIG. 3.In the depicted embodiment, an AC signal is generated by AC source 102and rectifier circuit 600 rectifies the AC signal and capacitor 603smoothes the signal such that a rectified and smoothed or filtered DCsignal is generated at DC output 106 at capacitor 603. The rectified andsmoothed DC signal at DC output 106 is received by power conversioncircuit 208 such that an output is generated at power conversion circuitoutput 210.

[0036] The input inductor 302 of embodiment FIG. 3, however, hasreplaced by two inductors 602 and 604. As shown, rectifier circuit 600is coupled between AC source 102 and inductors 602 and 604. In oneembodiment, the total inductance of inductors 602 and 604 is notnecessarily equal to the inductance of inductor 302. For instance, inone embodiment, one of the inductors 602 and 604 could be designedspecifically to have different impedance versus frequencycharacteristics than the other in order to filter specific EMIfrequencies more efficiently. In this embodiment either one or both ofinductors 602 and 604 can act as a fuse. Typically the lowest costsolution is to design only one of the inductors 602 and 604 to act as afuse in order that only one of the inductors 602 or 604 includes flameretardant or heatshrink covering to comply with international safetystandards as a fuse component.

[0037] In one embodiment, the circuit embodiment of FIG. 6 sharessimilar limitations as that of the circuit embodiment of FIG. 3 in termsof the input rectifier circuit 600. For instance, in one embodiment,rectifier circuit 600 must be a half wave rectifier circuit in order forthe use of either inductor 602 or 604 as a fuse to meet internationalsafety standards as previously described. Rectifier circuit 600 can,however, be a full wave rectifier circuit if a separate fuse componentis coupled between the AC source 102 and the input to rectifier circuit600.

[0038] In the foregoing detailed description, the present invention hasbeen described with reference to specific exemplary embodiments thereof.It will, however, be evident that various modifications and changes maybe made thereto without departing from the broader spirit and scope ofthe present invention. The present specification and figures areaccordingly to be regarded as illustrative rather than restrictive.

What is claimed is:
 1. A power supply input electromagnetic interference(EMI) filter circuit, comprising: an inductor to be coupled to analternating current (AC) source having an AC source capacitance; arectifier having an input coupled to the inductor, the inductor to becoupled between the AC source and the rectifier; and a capacitor coupledto an output of the rectifier such that an EMI pi filter is formed withthe AC source capacitance, the inductor and the capacitor.
 2. The powersupply EMI filter circuit of claim 1 wherein the capacitor is adapted toprovide bulk storage for a direct current (DC) input of a power supplyconversion circuit to be coupled to the capacitor.
 3. The power supplyEMI filter circuit of claim 2 wherein the power conversion circuit isadapted to provide an output power of less than approximately ten Watts.4. The power supply EMI filter circuit of claim 2 wherein the capacitorthat provides the bulk storage for the DC input of the power supplyconversion circuit consists of a single capacitor.
 5. The power supplyEMI filter circuit of claim 1 wherein the rectifier is half waverectifier circuit.
 6. The power supply EMI filter circuit of claim 5wherein the half wave rectifier circuit includes a plurality of inputsand a corresponding plurality of outputs, wherein the half waverectifier circuit comprises one or more diodes coupled between each ofthe inputs and the corresponding outputs of the half wave rectifiercircuit.
 7. The power supply EMI filter circuit of claim 1 wherein therectifier is a full wave rectifier circuit.
 8. The power supply EMIfilter circuit of claim 1 wherein the inductor is adapted to function asa fuse to limit an abnormal amount of current flow.
 9. The power supplyEMI filter circuit of claim 8 wherein the inductor is covered with aflame retardant material.
 10. The power supply EMI filter circuit ofclaim 8 wherein the inductor is covered with a heatshrink material. 11.A power supply input electromagnetic interference (EMI) filter circuit,comprising: a rectifier having an input to be coupled to an alternatingcurrent (AC) source having an AC source capacitance; an inductor havinga first terminal coupled to an output of the rectifier, the rectifier tobe coupled between the AC source and the first terminal of the inductor;and a capacitor coupled to a second terminal of the inductor such thatan EMI pi filter is formed with the AC source capacitance, the inductorand the capacitor.
 12. The power supply EMI filter circuit of claim 11wherein the capacitor is adapted to provide bulk storage for a directcurrent (DC) input of a power supply conversion circuit to be coupled tothe capacitor.
 13. The power supply EMI filter circuit of claim 12wherein the power conversion circuit is adapted to provide an outputpower of less than approximately ten Watts.
 14. The power supply EMIfilter circuit of claim 12 wherein the capacitor that provides the bulkstorage for the DC input of the power supply conversion circuit consistsof a single capacitor.
 15. The power supply EMI filter circuit of claim11 wherein the rectifier is half wave rectifier circuit.
 16. The powersupply EMI filter circuit of claim 15 wherein the half wave rectifiercircuit includes a plurality of inputs and a corresponding plurality ofoutputs, wherein the half wave rectifier circuit comprises one or morediodes coupled between each of the inputs and the corresponding outputsof the half wave rectifier circuit.
 17. The power supply EMI filtercircuit of claim 11 wherein the rectifier is a full wave rectifiercircuit.
 18. The power supply EMI filter circuit of claim 11 wherein theinductor is adapted to function as a fuse to limit an abnormal amount ofcurrent flow.
 19. The power supply EMI filter circuit of claim 18wherein the inductor is covered with a flame retardant material.
 20. Thepower supply EMI filter circuit of claim 18 wherein the inductor iscovered with a heatshrink material.
 21. A power supply inputelectromagnetic interference (EMI) filter circuit, comprising: a firstinductor to be coupled to a first line of an alternating current (AC)source having an AC source capacitance; a second inductor to be coupledto a second line of the AC source; a rectifier having first and secondinputs coupled to the first and second inductors, respectively, thefirst and second inductors to be coupled between the AC source and therectifier; and a capacitor coupled to an output of the rectifier suchthat an EMI filter is formed with the AC source capacitance, the firstand second inductors and the capacitor.
 22. The power supply EMI filtercircuit of claim 21 wherein the capacitor is adapted to provide bulkstorage for a direct current (DC) input of a power supply conversioncircuit to be coupled to the capacitor.
 23. The power supply EMI filtercircuit of claim 22 wherein the power conversion circuit is adapted toprovide an output power of less than approximately ten Watts.
 24. Thepower supply EMI filter circuit of claim 22 wherein the capacitor thatprovides the bulk storage for the DC input of the power supplyconversion circuit consists of a single capacitor.
 25. The power supplyEMI filter circuit of claim 21 wherein the rectifier is half waverectifier circuit.
 26. The power supply EMI filter circuit of claim 25wherein the half wave rectifier circuit includes a plurality of inputsand a corresponding plurality of outputs, wherein the half waverectifier circuit comprises one or more diodes coupled between each ofthe inputs and the corresponding outputs of the half wave rectifiercircuit.
 27. The power supply EMI filter circuit of claim 21 wherein therectifier is a full wave rectifier circuit.
 28. The power supply EMIfilter circuit of claim 21 wherein at least one or more of the first andsecond inductors are adapted to function as at least one or more fusesto limit an abnormal amount of current flow.
 29. The power supply EMIfilter circuit of claim 28 wherein the at least one or more of the firstand second inductors that are adapted to function as the at least one ormore fuses to limit the abnormal amount of current flow are covered witha flame retardant material.
 30. The power supply EMI filter circuit ofclaim 28 wherein the at least one or more of the first and secondinductors that are adapted to function as the at least one or more fusesto limit the abnormal amount of current flow are covered with aheatshrink material.
 31. A power supply input electromagneticinterference (EMI) filter circuit, comprising: a rectifier having aninput to be coupled to an alternating current (AC) source having an ACsource capacitance; a first inductor having a first terminal coupled toa first output of the rectifier; a second inductor having a firstterminal coupled to a second output of the rectifier, the rectifier tobe coupled between the AC source and the first and second inductors; anda capacitor coupled between a second terminal of the first inductor anda second terminal of the second inductor such that an EMI filter isformed with the AC source capacitance, the first and second inductorsand the capacitor.
 32. The power supply EMI filter circuit of claim 31wherein the capacitor is adapted to provide bulk storage for a directcurrent (DC) input of a power supply conversion circuit to be coupled tothe capacitor.
 33. The power supply EMI filter circuit of claim 32wherein the power conversion circuit is adapted to provide an outputpower of less than approximately ten Watts.
 34. The power supply EMIfilter circuit of claim 32 wherein the capacitor that provides the bulkstorage for the DC input of the power supply conversion circuit consistsof a single capacitor.
 35. The power supply EMI filter circuit of claim31 wherein the rectifier is half wave rectifier circuit.
 36. The powersupply EMI filter circuit of claim 35 wherein the half wave rectifiercircuit includes a plurality of inputs and a corresponding plurality ofoutputs, wherein the half wave rectifier circuit comprises one or morediodes coupled between each of the inputs and the corresponding outputsof the half wave rectifier circuit.
 37. The power supply EMI filtercircuit of claim 31 wherein the rectifier is a full wave rectifiercircuit.
 38. The power supply EMI filter circuit of claim 31 wherein theinductor is adapted to function as a fuse to limit an abnormal amount ofcurrent flow.
 39. The power supply EMI filter circuit of claim 38wherein the inductor is covered with a flame retardant material.
 40. Thepower supply EMI filter circuit of claim 38 wherein the inductor iscovered with a heatshrink material.
 41. A method, comprising: rectifyingan AC signal from an AC source; filtering the rectified AC signal with abulk storage capacitor to provide a DC signal to an input of a powerconversion circuit; and filtering the electromagnetic interference (EMI)generated by the power converter circuit with an EMI filter thatincludes an AC source capacitance of the AC source, one or moreinductors and the bulk storage capacitor.
 42. The method of claim 41wherein rectifying the AC signal comprises full wave rectifying the ACsignal with a full wave rectifier.
 43. The method of claim 41 whereinrectifying the AC signal from the AC source comprises half waverectifying the AC signal.
 44. The method of claim 41 further comprisinglimiting an abnormal amount of current from flowing with at least one ofsaid one or more inductors that are included in the EMI filter.
 45. Themethod of claim 44 further comprising covering the at least one of saidone or more inductors with a flame retardant material.
 46. The method ofclaim 44 further comprising covering the at least one of said one ormore inductors with a heatshrink material.